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INTERNATIONAL J OURNAL OF M ULTIDISCIPLINARY S CIENCES AND ENGINEERING, VOL . 2, NO. 6, S EPTEMBER 2011
Important Thermodynamic Concept
Amir Vosough1 and Sadeghvosough2
1,2
Department of Mechanics, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
[email protected]
Abstract— In this paper about the important concept of
thermodynamic as exergy, entropy, first and second law of
thermodynamic, industrial ecology and their application has
been discussed. In thermodynamics, the exergy of a system is the
maximum useful work possible during a process that brings the
system into equilibrium with a heat reservoir and entropy is a
thermodynamic property that can be used to determine the
energy available for useful work in a thermodynamic process,
such as in energy conversion devices, engines, or machines. The
first law of thermodynamics states that energy cannot be created
or destroyed and the second law of thermodynamics is an
expression of the tendency that over time, differences in
temperature, pressure, and chemical potential equilibrate in an
isolated physical system. Industrial Ecology (IE) is the study of
material and energy flows through industrial systems. The
global industrial economy can be modeled as a network of
industrial processes that extract resources from the Earth and
transform those resources into commodities which can be
bought and sold to meet the needs of humanity. Industrial
ecology seeks to quantify the material flows and document the
industrial processes that make modern society function.
Keywords– Thermodynamic, Concept, Exergy and Industrial
Ecology
combination property of a system and its environment
because unlike energy it depends on the state of both the
system and environment. The exergy of a system in
equilibrium with the environment is zero. Exergy is neither a
thermodynamic property of matter nor a thermodynamic
potential of a system. Exergy and energy both have units of
joules. The Internal Energy of a system is always measured
from a fixed reference state and is therefore always a state
function. Some authors define the exergy of the system to be
changed when the environment changes, in which case it is
not a state function. Other writers prefer a slightly alternate
definition of the available energy or exergy of a system where
the environment is firmly defined, as an unchangeable
absolute reference state, and in this alternate definition
exergy becomes a property of the state of the system alone.
The term exergy is also used, by analogy with its physical
definition, in information theory related to reversible
computing. Exergy is also synonymous with: availability,
available energy, exergic energy, essergy (considered
archaic), utilizable energy, available useful work, maximum
(or minimum) work, maximum (or minimum) work content,
reversible work, and ideal work. Summaries of the evolution
of exergy analysis are provided at [2-16].
I. INTRODUCTION
I
II. ENTROPY
n thermodynamics, the exergy of a system is the maximum
useful work possible during a process that brings the
system into equilibrium with a heat reservoir [1]. When the
surroundings are the reservoir, exergy is the potential of a
system to cause a change as it achieves equilibrium with its
environment. Exergy is the energy that is available to be
used. After the system and surroundings reach equilibrium,
the exergy is zero. Determining exergy was also the first goal
of thermodynamics. Energy is never destroyed during a
process; it changes from one form to another (see First Law
of Thermodynamics). In contrast, exergy accounts for the
irreversibility of a process due to increase in entropy (see
Second Law of Thermodynamics). Exergy is always destroyed
when a process involves a temperature change. This
destruction is proportional to the entropy increase of the
system together with its surroundings. The destroyed exergy
has been called anergy [1].
For an isothermal process, exergy and energy are
interchangeable terms, and there is no anergy. Exergy
analysis is performed in the field of industrial ecology to use
energy more efficiently. The term was coined by Zoran Rant
in 1956 but the concept was developed by J. Willard Gibbs in
1873 Ecologists and design engineers often choose a
reference state for the reservoir that may be different from
the actual surroundings of the system. Exergy is a
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Entropy is a thermodynamic property that can be used to
determine the energy available for useful work in a
thermodynamic process, such as in energy conversion
devices, engines, or machines. Such devices can only be
driven by convertible energy, and have a theoretical
maximum efficiency when converting energy to work.
During this work, entropy accumulates in the system, which
then dissipates in the form of waste heat. In classical
thermodynamics, the concept of entropy is defined
phenomenologically by the second law of thermodynamics,
which states that the entropy of an isolated system always
increases or remains constant. Thus, entropy is also a
measure of the tendency of a process, such as a chemical
reaction, to be entropically favored, or to proceed in a
particular direction. It determines that thermal energy always
flows spontaneously from regions of higher temperature to
regions of lower temperature, in the form of heat. These
processes reduce the state of order of the initial systems, and
therefore entropy is an expression of disorder or randomness.
This picture is the basis of the modern microscopic
interpretation of entropy in statistical mechanics, where
entropy is defined as the amount of additional information
needed to specify the exact physical state of a system, given
its thermodynamic specification. The second law is then a
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INTERNATIONAL J OURNAL OF M ULTIDISCIPLINARY S CIENCES AND ENGINEERING, VOL . 2, NO. 6, SEPTEMBER 2011
consequence of this definition and the fundamental postulate
of statistical mechanics. Thermodynamic entropy has the
dimension of energy divided by temperature
temperature, and a unit of
joules per kelvin (J/K) in the International System of Units
Units.
III. FIRST LAW OF THERMODYNAMICS
NAMICS
The first law of thermodynamics states that energy
cannot be created or destroyed. It is often expressed by the
statement that in a thermodynamic process the increment in
the internal energy of a system is equal to the increment of
heat supplied to the system, minus the increment of work
done by the system on its surroundings. The first law of
thermodynamics observes the principle of conservation of
energy. Energy can be transformed, i.e. changed from one
form to another, but cannot be created nor destroyed. The
first explicit statement of the first law of thermodynamics
referred to cyclic thermodynamic processes. It was made by
Rudolf Clausius in 1850:
In all cases in which work is produced by the agency of
heat, a quantity
tity of heat is consumed which is proportional to
the work done; and conversely, by the expenditure of an
equal quantity of work an equal quantity of heat is produced
produced.
Clausius stated the law also in another form, this time
referring to the existence of a function of state of the system
called the internal energy, and expressing himself in terms of
a differential equation for the increments of a thermodynamic
process. This equation may be translated into words as
follows:
In a thermodynamic process, the inc
increment in the
internal energy of a system is equal to the difference between
the increment of heat accumulated by the system and the
increment of work done by it.
whereδQ and δW are infinitesimal amounts of heat supplied
to the system and work done by the system, respectively.
Note that the minus sign in front of δW indicates that a
positive amount of work done by the system leads to energy
being lost from the system. (An alternate convention is to
consider the work performed on the system by its
surroundings. This leads to a change in sign of the work. This
is the convention
onvention adopted by many modern textbooks of
physical chemistry, such as those by Peter Atkins and Ira
Levine, but many textbooks on physics define work as work
done by the system.)When
When a system expands in a quasistatic
process,, the work done on the environment is the product of
pressure (P) and volume (V)) change, i.e. PdV, whereas the
work done on the system is -PdV
V. The change in internal
energy of the system is:
(2)
Work and heat are expressions of actual physical
processes which add or subtract energy, while U is a
mathematical abstraction that keeps account of the exchanges
of energy
nergy that befall the system. Thus the term heat for δQ
means that amount of energy added as the result of heating,
rather than referring to a particular form of energy. Likewise,
work energy for δW means "that amount of energy lost as the
result of work". Internal energy is a property of the system
whereas work done and heat supplied are not. A significant
result of this distinction is that a given internal energy change
dU can be achieved by, in principle, many combinations of
heat and work.The internal energy
nergy of a system is not uniquely
defined. It is defined only up to an arbitrary additive constant
of integration, which can be adjusted to give arbitrary
reference zero levels. This non-uniqueness
uniqueness is in keeping with
the abstract mathematical nature of the internal energy.
A. Description
The first law of thermodynamics was expressed in two
ways by Clausius. One way referred to cyclic processes and
the inputs and outputs of the system, but did not refer to
increments in the internal state of the system. The other way
referred to any incremental change in the internal state of the
system, and did not expect the process to be cyclic. A cyclic
process is one which can be repeated indefinitely often and
still eventually leave the system in its original state.
In each repetition of a cyclic process, the work done by
the system is proportional to the heat consumed by the
system. In a cyclic process in which the system does work on
its surroundings, it is necessary that some heat be taken in by
the system and some be put out, and the difference is the heat
consumed by the system in the process. The constant of
proportionality
onality is universal and independent of the system
and was measured by Joule in 1845 and 1847.
In any incremental process, the change in the internal
energy is considered
ered due to a combination of heat added to
the system and work done by the system. Taking dU as an
infinitesimal
initesimal (differential) change in internal energy, one
writes
(1)
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IV. SECOND LAW OF THERMODYNAMICS
THERMOD
The second law of thermodynamics is an expression of
the tendency that over time, differences in temperature,
pressure, and chemical potential equilibrate in an isolated
physical system.. From the state of thermodynamic
equilibrium, the law deduced the principle of the increase of
entropy and explains the phenomenon of irreversibility in
nature. The second law
w declares the impossibility of
machines that generate usable energy from the abundant
internal energy of nature by processes called perpetual
motion of the second kind. The second
econd law may be expressed
in many specific ways, but the first formulation is credited to
the German scientist Rudolf Clausius.
Clausius The law is usually
stated in physical terms of impossible processes. In classical
thermodynamics,, the second law is a basic postulate
applicable
licable to any system involving measurable heat transfer,
while in statistical thermodynamics,
thermodynamics the second law is a
consequence of unitarity in quantum theory.
theory In classical
thermodynamics, the second law defines the concept of
thermodynamic entropy,, while in statistical mechanics
entropy is defined from information theory,
theory known as the
Shannon entropy.
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INTERNATIONAL J OURNAL OF M ULTIDISCIPLINARY S CIENCES AND ENGINEERING, VOL . 2, NO. 6, SEPTEMBER 2011
A. Description
The first law of thermodynamics provides the basic
definition of thermodynamic energy, also called internal
energy, associated with all thermodynamic systems
systems, but
unknown in mechanics, and states the rule of conservation of
energy in nature.
However, the concept of energy in the first law does not
account
unt for the observation that natural processes have a
preferred direction of progress. For example, spontaneously,
heat always flows to regions of lower temperature, never to
regions of higher temperature without external work being
performed on the system.. The first law is completely
symmetrical with respect to the initial and final states of an
evolving system. The key concept for the explanation of this
phenomenon through the second law of thermodynamics is
the definition of a new physical property, the entropy. A
change in the entropy (S)) of a system is the infinitesimal
transfer of heat (Q)) to a closed system driving a reversible
process, divided by the equilibrium temperature ((T) of the
system.
(3)
The entropy of an isolated system that is in equilibrium
is constant and has reached its maximum value. Empirical
temperature and its scale is usually defined on the principles
of thermodynamics equilibrium by the zeroth law of
thermodynamics.. However, based on the entropy, the second
law permits a definition of the absolute, thermodynamic
temperature, which has its null point at absolute zero
zero. The
second law of thermodynamics may be expressed in many
specific ways, the most prominent classical statements[3]
being the original statement by Rudolph Clausius (1850), the
formulation by Lord Kelvin (1851), and the definition in
axiomatic thermodynamics by Constantin Carathéodory
(1909). These statements cast the law in general physical
terms citing the impossibility of certain processes. They have
been shown to be equivalent [17].
No process is possible in which the sole
sol result is the
absorption of heat from a reservoir and its complete
conversion into work.
This means it is impossible to extract energy by heat
from a high-temperature
temperature energy source and then convert all
of the energy into work. At least some of the energy must be
passed on to heat a low-temperature
temperature energy sink. Thus, a heat
engine with 100% efficiency is thermodynamically
impossible. This also means that it is impossible to build
solar panels that generate electricity solely from the infrared
band of the electromagnetic
lectromagnetic spectrum without consideration
of the temperature on the other side of the panel (as is the
case with conventional solar panels that operate in the visible
spectrum).Note that it is possible to convert heat completely
into work, such as the isothermal expansion of ideal gas.
gas
However, such a process has an additional result. In the case
of the isothermal expansion, the volume of the gas
g increases
and never goes back without outside interference.
D. Principle of Carethedory
Constantin Carathéodory formulated thermodynamics on
a purely
ely mathematical axiomatic foundation. His statement of
the second law is known as the Principle of Carathéodory,
which may be formulated as follows:
In every neighborhood of any state S of an adiabatically
isolated system there are states inaccessible from
fro S.
With this formulation he described the concept of
adiabatic accessibility for the first time and provided the
foundation for a new subfield of classical thermodynamics,
often called geometrical thermodynamics [17].
Equivalence of the statements Derive Kelvin Statement
from Clausius Statement. Suppose there is an engine
violating the Kelvin statement: i.e., one that drains heat and
converts it completely into work in a cyclic fashion without
any other result. Now pair it with a reversed Carnot engine as
shown by the graph. The net and sole effect of this newly
created engine consisting of the two engines mentioned is
(4)
B. Clausius Statement
German scientist Rudolf Clausius is credited with the
first formulation of the second law, now known as the
Clausius statement:
No process is possible whose sole result is the transfer of
heat from a body of lower temperature to a body of higher
temperature.
Spontaneously, heat cannot flow from cold regions to hot
regions without external work being performed on the
system, which is evident from ordinary experience of
refrigeration, for example. In a refrigerator,
tor, heat flows from
cold to hot, but only when forced by an external agent, a
compressor.
C. Kelvin Statement
Lord Kelvin expressed the second law in another form.
The Kelvin statement expresses it as follows:
Fig. 1: Cooler
ooler reservoir to the hotter one, which violates the Clausius
statement
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INTERNATIONAL J OURNAL OF M ULTIDISCIPLINARY S CIENCES AND ENGINEERING, VOL . 2, NO. 6, S EPTEMBER 2011
transferring heat from the cooler reservoir to the hotter one
(Fig. 1), which violates the Clausius statement. Thus the
Clausius statement implies the Kelvin statement. We can
prove in a similar manner that the Kelvin statement implies
the Clausius statement, or, in a word, the two are equivalent.
V. INDUSTRIAL ECOLOGY
Industrial Ecology (IE) is the study of material and
energy flows through industrial systems. The global industrial
economy can be modeled as a network of industrial processes
that extract resources from the Earth and transform those
resources into commodities which can be bought and sold to
meet the needs of humanity. Industrial ecology seeks to
quantify the material flows and document the industrial
processes that make modern society function [18]. Industrial
ecologists are often concerned with the impacts that industrial
activities have on the environment, with use of the planet's
supply of natural resources, and with problems of waste
disposal. Industrial ecology is a young but growing
multidisciplinary field of research which combines aspects of
engineering, economics, sociology, toxicology and the
natural sciences. Industrial Ecology has been defined as a
"systems-based, multidisciplinary discourse that seeks to
understand emergent behavior of complex integrated
human/natural systems". The field approaches issues of
sustainability by examining problems from multiple
perspectives, usually involving aspects of sociology, the
environment, economy and technology. The name comes
from the idea that we should use the analogy of natural
systems as an aid in understanding how to design sustainable
industrial systems. Industrial Ecology (IE) is the study of
material and energy flows through industrial systems. The
global industrial economy can be modeled as a network of
industrial processes that extract resources from the Earth and
transform those resources into commodities which can be
bought and sold to meet the needs of humanity. Industrial
ecology seeks to quantify the material flows and document
the industrial processes that make modern society function.
Industrial ecologists are often concerned with the impacts that
industrial activities have on the environment, with use of the
planet's supply of natural resources, and with problems of
waste disposal. Industrial ecology is a young but growing
multidisciplinary field of research which combines aspects of
engineering, economics, sociology, toxicology and the
natural sciences. Industrial Ecology has been defined as a
"systems-based, multidisciplinary discourse that seeks to
understand emergent behavior of complex integrated
human/natural systems". The field approaches issues of
sustainability by examining problems from multiple
perspectives, usually involving aspects of sociology, the
environment, economy and technology. The name comes
from the idea that we should use the analogy of natural
systems as an aid in understanding how to design sustainable
industrial systems. Industrial ecology was popularized in
1989 in a Scientific American article by Robert Frosch and
Nicholas E. Gallopoulos.
Frosch and Gallopoulos' vision was "why would not our
industrial system behave like an ecosystem, where the wastes
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of a species may be resource to another species? Why would
not the outputs of an industry be the inputs of another, thus
reducing use of raw materials, pollution, and saving on waste
treatment?" A notable example resides in a Danish industrial
park in the city of Kalundborg. Here several linkages of
byproducts and waste heat can be found between numerous
entities such as a large power plant, an oil refinery, a
pharmaceutical plant, a plasterboard factory, an enzyme
manufacturer, a waste company and the city itself. The
scientific field Industrial Ecology has grown quickly in recent
years [19]. The Journal of Industrial Ecology (since 1997),
the International Society for Industrial Ecology (since 2001),
and the journal Progress in Industrial Ecology (since 2004)
give Industrial Ecology a strong and dynamic position in the
international scientific community. Industrial Ecology
principles are also emerging in various policy realms such as
the concept of the Circular Economy that is being promoted
in China. Although the definition of the Circular Economy
has yet to be formalized, generally the focus is on strategies
such as creating a circular flow of materials, and cascading
energy flows. An example of this would be using waste heat
from one process to run another process that requires a lower
temperature. The hope is that strategy such as this will create
a more efficient economy with fewer pollutants and other
unwanted by products [20].
VI.
CONCULATION
In this paper about the important concept of
thermodynamic as exergy, entropy, the first and second law
of thermodynamic, industrial ecology and their application
has been discussed. Industrial Ecology (IE) is the study of
material and energy flows through industrial systems. The
global industrial economy can be modeled as a network of
industrial processes that extract resources from the Earth and
transform those resources into commodities which can be
bought and sold to meet the needs of humanity. Industrial
ecology seeks to quantify the material flows and document
the industrial processes that make modern society function.
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